Electrostatic separator with coated discharge electrode



Dec.'20, 1966 T. M. KORZEKWA 3,292,736

ELECTROSTATIC SEPARATOR WITH COATED DISCHARGE ELECTRODE 2 Sheets-Sheet 1 Filed Sept. 5, 1963 FIG! Inventor 3,292,786 ELECTROSTATIC SEPARATOR WITH COATED DISCHARGE ELECTRODE Filed Sept. 5, 1965 Dec. 20, 1966 T. M? KORZEKWA V 2 Shee ts-Sheet 2 United States Patent 6 3,292,786 ELECTROSTATIC SEPARATOR WITH COATED DISCHARGE ELECTRODE Tadeusz Mieczyslaw Korzekwa, Toronto, Ontario, Canada, assignor to Ontario Research Foundation, Toronto,

Ontario, Canada Filed Sept. 5, 1963, Ser. No. 306,898 7 Claims. (Cl. 209-429) The invention relates to an electrostatic separator having an improved electrode.

Electrostatic separators of various kinds are well known for the separation of comminuted or powdered materials such as crushed ore, in which material is fed on to a rotating drum and subjected to electrostatic charge causing such particles to fall from the drum at different points dependent upon their electrostatic properties. 7

In such apparatus the drum is usually formed of brass and provides one electrode, the other being frequently a so-called brush electrode comprising a row of sharppointed conductors directed at the drum. The location of f However, as the static charge which can be applied to crushed or powdered material. An improved form of this apparatus utilizes aneon discharge tube for, attracting some of the particles from the drum after they have become charged by passage through the corona discharge from the brush electrode. In this way the degree of separation is improved since the neon tube will attract some particles more strongly than others and thus acts to accentuate the effect of gravity on such particles. In this Way the effect of the limitation as to the maximum voltage which can be used at the brush electrode has been somewhat offset, but obviously it is nonetheless advantageous to improve the quality of the corona discharge and to raise still further the voltage thereof and thus further improve the quality of separation achieved.

Attempts have been made to improve such discharge by providing a substantial non-conducting enclosure or shield for the electrode, and also by applying a varying potential thereto, and also by utilizing electrodes of various shapes, but such attempts have generally failed to achieve significant improvements and have sometimes been subject to variation in the degree of separation achieved.

Accordingly it is an object of the invention to provide a high tension electrostatic separator having an improved electrode enabling operation at increased levels of efficiency.

More particularly it is an object of the invention to provide a separator having the foregoing advantages which is adapted for operation at higher voltages.

More particularly it is an object of the invention to provide a separator having the foregoing advantages in which the quality of the electrostatic corona discharge'is enhanced.

More particularly it is an object of the invention to provide a separator having the foregoing advantages which is operable effectively with a wide variety of materials and grades of material.

' A preferred embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which like references refer to like parts thereof throughout the various views and diagrams and in which;

FIGURE 1 is a diagramatic side elevation partially in section showing the general construction of the separator according to the invention;

FIGURE 2 is a perspective view of part of the improved electrode of the instant separator, enlarged for clarity; and,

FIGURE 3 is a section along the length of the electrode of FIGURE 2', still further enlarged.

In FIGURE 1 the separator according to the invention will be seen to comprise hopper 10 containing the comminuted or powdered material, in this case being crushed iron ore and consisting principally of hematite particles 11 and silica particles 12, feeding on to chute 13 which is directed downwardly to permit such particles to flow therealong under the influence of gravity. Chute 13 terminates at lower end 14 situated at approximately the highest point of drum 15 substantially vertically above axis 16 thereof. Electrostatic shield 17 is located adjacent to chute 13 close to said lower end 14 and prevents particles thereon from acquiring an electrostatic charge which would otherwise restrict the natural flow thereof under gravita tional force as aforesaid.

Drum 15 is rotatable slowly to carry particles 11 and 12 thereon around an arcuate path defined by the periphery of drum 15. After about 20 degrees of rotation, that is to say at approximately 340 degrees, assuming the topmost point of drum 15 to be 360 degrees, particles 11 and 12 are exposed to an electrostatic corona'discharge from electrode 18 which is supported in position between insulated support member 19 and is supplied with a high potential charge by high-tension wire 20. After a further 60 degrees of rotation neon tube 21 is located spaced from the surface of drum 15 and supported on insulated support members 22 and being also supplied 'with high potential current by means of wire 20. Support members 19 and 22 are movable to adjust the location of electrode 18 and neon tube 21 relative to the surface of drum 15 and relative to one another to ensure maximum separation in any particular case.

Situated beneath drum 15 are three bins for collecting the separated particles and comprising concentrate bin 23 middlings bin 24 and tailings bin 25. The location of bins 23, 24 and 25 is such as to ensure the collection of the separated hematite particles 11 in maximum concentration in bin 23 and a mixture of hematite particles 11 and silica particles 12 in bin 24 and substantially no hematite particles 11 in bin 25. Blades 26 and 27 are hinged for movement as desired to achieve optimum separation for any particular case. Rotary brush 28 is located in contact with the surface of drum 15 and is driven by means not shown in a direction contrary to the rotation of drum 15 to ensure substantial removal of all particles after a total of approximately 270 degrees of rotation.

It will, of course, be appreciated that as in other separators of this type drum 15 is made of brass or other suitable material and constitutes an electrode upon which particles 11 and 12 are retained by the electrostatic charge applied thereto and is connected in circuit with the negative side of a power source not shown, the positive side of which is connected through wire 20 to neon tube 21 and the electrode 18.

Turning now to FIGURES 2 and 3 it will be noted that electrode 18 according to this preferred embodiment of the invention comprises the wire core 29 of drawn copper or like material surrounded by a thin coating of insulating material 30 may be such that the coating is of a thickness of between 1 and 5 percent of the diameter of the wire, and such as shellac. The relative dimensions of wire 29 insulating material 30 similar to those of, for example, wire used for winding coils, and may typically be about 0.010 inch diameter for the wire about 0.0002 inch in thickness for the insulating material making a total overall diameter of 0.0104 inch for the entire electrode. It will 'be noted from FIGURES 2 and 3 that insulating material 30 is of a substantially porous nature and is in fact characterized by a large number of fine hairline cracks 31 or fissures extending through insulating material 30 and exposing minute areas of wire core 29. Such cracks may in some cases be continuous around the profile of electrode 18 but are more typically, a series of discontinuous cracks extending around only a portion thereof. The dimensions of such cracks are irregular and of a random nature and in this preferred embodiment may be of a width of as little as approximately one micron or even less in some cases. In addition, the surface of wire core 29 should preferably be highly polished to avoid any surface irregularities or discontinuities such as would tend to concentrate the discharge at any particular point therealong. A suitable electrode 18 may be manufactured according to this preferred embodiment of the invention by selecting a length of wire of suitable dimensions which has previously been polished and coated in known manner with a shellac coating baking such length of wire for about twenty minutes, or in any event long enough to render the shellac coating hard and brittle and subsequently stretching the wire slightly to provide the hairline cracks 21, the degree of stretching required being in the order of about one to five per cent of its length, thus making the total area of the cracks about one to five per cent of the total surface area of the wire, the cracks being randomly spaced therealong.

The operation of the instant separator proceeds in conventional manner that is to say particles 11 and 12 are fed on to drum 15 rotating at approximately 220 r.p.m. in an anti-clockwise direction. A potential of between 20,000 and 30,000 volts is applied to wire passing through neon tube 21 and creating an electrostatic corona discharge from electrode 18 on to the surface of drum 15 thereby applying an electrostatic charge to particles 11 and 12. Particles 11 and 12 will adhere to drum 15 and as they pass by neon tube 21 hematite particles 11 being attracted thereto more strongly will become separated from drum 15 and fall into bin 23. Silica particles 12 together with a small proportion of hematite particles 11 will however remain adhered to drum 15 and will be carried therearound, some of them falling in bin 24, including the majority of the remaining hematite particles 11 and the remainder of them being brushed from drum 15 by brush 28 and falling into bin including, substantially pure silica particles 12. The potential applied to electrode 18 and the distance of separation of electrode 18 from drum 15 are found to be increased in each case and the quality of the corona discharge from electrode 18 is both more uniform and more stable, the voltage stresses being concentrated at the pores or cracks 31. .Notwithstanding the increased voltage and separation of electrode 18 however insulating material is found to be substantially undamaged by the corona discharge and a significant reduction was noted in the tendency to arcing.

In addition, the increased voltage and separation of electrode 18 from drum 15 in turn increased the voltage applied to the neon tube 21 thereby further improving its lifting power on hematite particles 11.

In addition, the bouncing of particles 11 and 12 on drum 15 was significantly diminished and, by reason of the greater spacing between electrode 18 and drum 15 there was less danger of mechanical damage to insulating material 30 and there was less danger of sharp-edge particles becoming pinned to electrode 18 and causing arcing.

While the copper wire core 29 and shellac insulating material 30 have been found to be particularly suitable according to this preferred embodiment of the example, other ma er al-1. may also have been tested and are found to give adequate performance in certain circumstances. Thus both a tungsten wire core of a diameter of 0.014 inch and a piano wire of 0.008 inch have been found to give good results according to the following table of comparison:

Electrode Cooper Cooper Tung- Piano Wire Wire sten Wire Wire Percent Si02 0. 03 0.09 0.38 0.18

% S102 Remover? 99. 1 97.4 88. 3 94.3

In a single pass.

The foregoing is a description of a preferred embodiment of the invention which is here made 'by way of example only. The invention is not to be taken as limited to any of the specific features disclosed but comprehends all such variations as come within the spirit and scope of the appended claims.

What I claim is:

1. An electrostatic separator apparatus for separation of comminuted materials and comprising: rotary electrode means carrying said comminuted materials about an arcuate path; feed means oriented to direct said comminuted materials onto said rotary electrode means; collector means located adjacent said rotary electrode to receive said comminuted materials therefrom; a dis- 1 charge electrode wire located in spaced relation to said rotary electrode for establishing an electrostatic discharge therebetween; and an insulating material around said wire defining a coating characterized by a series of fine cracks.

2. An electrostatic separator apparatus for separation of comminuted materials and comprising rotary electrode means carrying said comminuted materials about an arcuate path; feed means oriented to direct said comminuted materials onto said rotary electrode means; collector of comminuted materials and comprising: rotary elec-.

trode means carrying said comminuted materials about an arcuate path; feed means oriented to direct said comminuted materials onto said rotary electrode means; col-' lector meanslocated adjacent said rotary electrode to receive said comminuted materials therefrom; a discharge electrode wire located in spaced relation to said rotary electrode for establishing an electrostatic discharge therebetween; and, a coating of insulating material around said wire, said coating having a plurality of small openings therein exposing portions of said wire, said openings totaling not more than about 1 to 5 percent of the total surface area of said wire and being randomly spaced therealong.

4. An electrostatic separator apparatus for separation of comminuted materials and comprising: rotary electrode means carrying said comminuted materials about an arcuate path; feed means oriented to direct said comminuted materials onto said rotary electrode means; collector means located adjacent said rotary electrode to receive said comminuted materials therefrom; a discharge electrode wire located in spaced relation to said rotary electrode for establishing an electrostatic discharge therebetween; and, a discontinuous coating of insulating material around said wire said discontinuities being constituted by a plurality of fine cracks in said coating randomly spaced along said wire and of a width of about 1 micron.

5. An electrode separator apparatus for separation of comminuted materials and comprising: rotary elec trode means carrying said comminuted materials about an arcuate path; feed means oriented to direct said comminuted materials onto said rotary electrode means; collector means located adjacent said rotary electrode to receive said comminuted materials therefrom; a discharge electrode wire located in spaced relation to said rotary electrode for establishing an electrostatic discharge therebetween; and, a discontinuous coating of shellac material around said wire heat-treated to render the same brittle and said discontinuities being constituted by a plurality of fine cracks in said coating randomly spaced along said wire.

6. An electrostatic separator apparatus for separation of comminuted materials and comprising; rotary electrode means carrying said comminuted materials about an arcuate path; feed means oriented to direct said comminuted materials onto said rotary electrode means; collector means located adjacent said rotary electrode to receive said comminuted materials therefrom; a discharge electrode Wire located in spaced relation to said rotary electrode for establishing an electrostatic discharge therebetween, said wire being highly polished to remove surface irregularities thereon; and an insulating material around said wire defining a coating characterized by a series of fine cracks, said coating being of a thickness of between 1 and 5 percent of the diameter of said wire.

7. An electrostatic separator apparatus for separation of comminuted materials and comprising: rotary electrode means carrying said comminuted materials about an arcuate path; a neon discharge tube located adjacent said rotary electrode; feed means oriented to direct said comminuted materials onto said rotary electrode means, an electrostatic shield adjacent said feed means; collector means located adjacent said rotary electrode to receive said comminuted materials therefrom; means continually brushing said rotary electrode, a discharge electrode wire located in spaced relation to said rotary electrode for establishing an electrostatic discharge therebetween; and an insulating material around said wire defining a coating characterized by a series of fine cracks, said coating being of a thickness of between 1 and 5 percent of the diameter of said wire.

References Cited by the Examiner UNITED STATES PATENTS 2,187,637 1/1940 Sutton 209--l29 3,012,668 12/1961 Fraas 209127 3,031,079 4/1962 Boss 209-128 FRANK W. LUTIER Primary Examiner 

1. AN ELECTROSTATIC SEPARATOR APPARATUS FOR SEPARATION OF COMMINUTED MATERIALS AND COMPRISING: ROTARY ELECTRODE MEANS CARRYING SAID COMMINUTED MATERIALS ABOUT AN ARCUATE PATH; FEED MEANS ORIENTED TO DIRECT SAID COMMINUTED MATERIALS ONTO SAID RETORY ELECTRODE MEANS; COLLECTOR MEANS LOCATED ADAJACENT SAID ROTARY ELECTRODE TO RECEIVE SAID COMMINUTED MATERIALS THEREFROM; A DISCHARGE ELECTRODE WIRE LOCATED IN SPACED RELATION TO SAID ROTARY ELECTRODE FOR ESTABLISHING AN ELECTROSTATIC DISCHARGE THEREBETWEEN; AND AN INSULATING MATERIAL AROUND SAID WIRE DEFINING A COATING CHARACTERIZED BY A SERIES OF FINE CRACKS. 